Nano-enabled Energy
Conversion, Storage and Thermal Management Systems (NEXT) Group
Director: Dr. Ronggui Yang, Associate
Professor of Mechanical Engineering
Office Location: ECME 136,
Post-Doctor Offices: ECME
251A, ECME 251B
Student
Offices and Labs: ECME 165, ECME 219
Tel: 303-735-1003 (O), 303-735-1763
(Lab); Fax: 303-492-3498
People Research Publications Facilities Open Positions News
Currently our research spans over developing
numerical/theoretical and experimental tools for understanding nanoscale thermal and thermoelectric transport, probing new
transport phenomena in nanocomposites, hybrid inorganic-organic crystals, and
hybrid micro/nano-structures, and applying the discoveries in fundamental
sciences at micro/nano-scales to thermal management and energy
conversion/storage systems. To better reflect the expertise and the research
activities of our multi-disciplinary research team, in September 2009 we
re-named our “Nanoscale and Ultrafast Thermal
Sciences and Applications (NUTS)” group established in January 2006 to
“Nano-enabled Energy Conversion, Storage, and Thermal Management systems
(NEXT)” group.
A) SELECTED RESEARCH AREAS:
1. Modeling and Simulation of Nanoscale Thermal and Thermoelectric
Transport:
As the size of structures approaches
the nanoscale, the conventional Fourier law of heat conduction does not remain
applicable. We are interested in understanding how heat transfer in
nanostructures differs from that in macrostructures and how to model and
predict the heat transfer in nanostructures. We have developed the
deterministic (discrete ordinate method and finite volume method) and
stochastic (
2. Soft X-ray for Probing Nanoscale and Ultrafast Thermal Transport:
Femtosecond
laser is a unique tool to study a number of ultrafast relaxation processes and
nanoscale phenomena. We have constructed a femtosecond two color (blue &
near-infrared) pump-probe system with 8 ns delay time with the aim to extract
the phonon relaxation time and phonon reflectivity at interfaces which are
essential parameter inputs for nanoscale thermal transport
modeling/simulations. This experiment system is now on daily operation for
studying electron energy relaxation, phonon energy relaxation, and
electron-phonon coupling in bulk and nanostructured materials. Collaborating
with ourphysics colleagues Professor Margaret Murnane
and Professor Henry Kapteyn of JILA/physics at
CU-Boulder, we have been constructing a pump-probe system using the table-top
femtosecond soft X-ray beams. The soft X-ray offers many advantages over
visible or infrared light due to its short wavelength (selective wavelength of
2-30nm). We have recently used the change in diffraction from
micro/nanostructured gratings to directly observe the transition between
diffusive and ballistic heat transport. The initial report of this
groundbreaking work in CLEO conference has attracted a lot of interest and was
highlighted as one of the 5 CLEO Technical News Summaries (May 2008) and later
was highlighted again as one of the 4 Physics Update items in the July 2008
issue of Physics Today, the membership magazine of the 120,000-member American
Institute of Physics. p.17 (July 2008). Very recently, a journal paper
reporting this experimental observation has been published by Nature Materials.
The
experimental system we developed enables us to further understand nanoscale and
ultrafast thermal transport fundamentals. Currently we focus on demonstrating
the possibility of using soft X-ray to image thermal transport with nanoscale
spatial and picosecond temporal resolutions simultaneously. The success of such
an implementation will enable us to watch how thermal energy is dissipated in
the drain side of nanoscale transistors, how the heat is propagated through an
interface of dissimilar materials, how the heat is generated and transported
surrounding nanoparticles in a variety of
environment.
3.
Micro/Nano-Enabled Thermal Management
The scaling down of feature sizes
in microelectronic devices leads to an increase in heat dissipation per unit
volume that consequently may affect device performance and reliability. A very
similar concern arises in the design of high power semiconductor lasers in
which heat generation can become extreme. Further, the energy conversion
technologies also rely on efficient thermal management. For example, the external thermal management solutions boost the efficiencies of
thermo-photovoltaics and solar cells by increasing
the heat removal capability. Nanotechnology not only creates hurdles but also
solutions for thermal management. Working with our colleagues Professor YC Lee,
Professor Victor Bright and Professor Steven George of CU-Boulder and Professor
Chen Li and Professor G.P. Peterson, we conceptualized the possibility to build
flexible thermal ground planes that have 100 times better thermal conductivity
than diamond, the best natural thermal conducting material, by utilizing phase
change heat transfer in hybrid micro/nano- wicking structures encased in
millimeter-thick polymer chamber. Such an innovation will enable a new
generation of high-performance, integrated microelectronic, power conversion,
photonic or microwave systems operating at high power density without
constraints resulting from complex thermal management solutions. The key to our
innovation is manufacturable micro/nanotechnologies
for low-cost applications and the in-depth understanding of phase change heat
transfer. We will significantly further the understanding of how
micro/nano-structures could improve phase change heat transfer by this study.
4. Nano-Enabled Thermoelectric Energy
Conversion
One of our most successful applications in tailoring transport properties is nano-thermoelectrics, for which we use nanotechnologies to engineer structures to have thermal conductivity lower than alloys while maintaining electron power factor (electrical conductivity times the square of thermoelectric Seebeck coefficient), which is not achievable in bulk materials. Collaborating with Professor Gang Chen and Professor Mildred Dresselhaus who are pioneers in nanostructured thermoelectrics, we laid out the theoretical foundation for proposing nanocomposites as high efficient thermoelectric materials during my Ph.D study at MIT. Our nanocomposite work brought in a paradigm-shift to thermoelectric research from the proof-of-concept demonstration to a potential commercial product since nanocomposites can be cost-effectively fabricated to realize nano-enabled efficiency enhancement. Our current work on thermoelectrics include: 1) modeling and characterization of thermal, thermoelectric, and electrical transport in various thermoelectric nanostructures, 2) developing periodic quantum dot nanocomposites that are low-cost but could potentially have similar efficiency as superlattices, 3). developing integrated thermoelectric systems for solar-electricity, waste heat recovery and thermal management.
5. Nano-Enabled Electrodes for Lithium Ion
Batteries (Details coming soon)
We are also working on 3-dimensional nanostructures for lithium ion battery electrode and photovoltaic applications. An interesting project that we are pursuing is the on-chip integration of silicon-nanowire array-enabled photovoltaic and lithium ion batteries which could provide potentially 24-hour uninterrupted solar power-supply.
B). RESEARCH
AWARDS (to PI Professor Ronggui Yang):
2011 Steve Woodward Outstanding Faculty Award, Department of Mechanical Engineering, CU-Boulder
2010 ASME Bergles-Rohsenow Young Investigator Award in Heat Transfer
(The Bergles-Rohsenow Young Investigator Award in
Heat Transfer is given to a young engineer who is under 36 and has received a
Ph.D., or an equivalent degree in engineering. Citation for this award: For developing modeling and experimental tools to
understand micro/nanoscale thermal transport and for
innovative applications of micro/nano-structure in macroscale forms for energy conversion and thermal
management. ASME
Press Release)
2010
Dean’s Award for the Outstanding Junior Faculty Member, College of Engineering
and Applied Science, University of Colorado
2010 Biography featured as a technology developer with outstanding potential that could reverse the decline in the book “The Rise and Fall of American Technology” by Dr. Lynn G. Gref.
2009 National Science Foundation (NSF) CAREER Award (the National Science Foundation's most prestigious awards in support of junior faculty who exemplify the role of teacher-scholars through outstanding research, excellent education and the integration of education and research within the context of the mission of their organizations.)
2009 Selected as one of
the <100 Invited Participants, the US
National Academy of Engineering's (NAE) 15th U.S. Frontiers of
Engineering Symposium. US
NAE Press Release.
2008 Technology Review’s TR35 Award (one of the 35 young scientists and technologists in world who are under the age of 35, but their work--spanning medicine, computing, communications, electronics, nanotechnology, energy, and more--is changing our world.) TR35 Profile, US AFOSR Press Release, CU Press Release
2008 DARPA/MTO Young Faculty Award (one of the 39 rising stars in university microsystems research), DARPA Press Release, CU Press Release
2008-2011 Sanders Faculty
Fellow,
2008 Outstanding Research Award, Department of Mechanical Engineering, CU-Boulder.
2008 Nominated for IEEE/ACM William J. McCalla ICCAD 2008 Best Paper Award by the conference organizers of the 2008 International Conference on Computer-Aided Design (ICCAD).
2005 Best Paper Award – Research, InterPACK 2005 (the ASME/Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems), 1 out of 500+ papers.
2005 Goldsmid Award for Excellence in Research in Thermoelectrics, International Thermoelectrics Society.
2004 NASA Certificate of Recognition for a Technical Innovation (Space Act Tech Brief Award), NASA Inventions and Contributions Board.
2003 Elected full member of Sigma Xi, the Scientific Research Society.
C). AWARDS RECEIVED BY
THE ADVISEES (Check out the People Page):